The present invention relates to a vehicle internal combustion engine arrangement, and more specifically to such an arrangement comprising a waste heat recovery system.
For many years, attempts have been made to improve the efficiency of internal combustion engines, which has a direct impact on fuel consumption.
For this purpose, it has long been proposed to provide vehicles with an engine arrangement equipped with a waste heat recovery system, i.e. a system making use of the thermal energy which is contained in hot exhaust gases or in other engine hot fluids and which would otherwise be lost.
One example of a waste heat recovery system is a Rankine circuit.
In such a circuit, a working fluid flows in a closed loop and undergoes successive processes according to the Rankine thermodynamic cycle:                the working fluid, which is a liquid at this stage, is pumped or compressed from low to high pressure;        the high pressure working liquid is evaporated into a gas by a hot engine fluid flowing in another circuit of the engine arrangement;        the working gas is expanded in an expander;        finally, the working gas is condensed.        
As a result, at least part of the thermal energy of the hot fluid used to evaporate the Rankine fluid is recovered in the expander under the form mechanical energy. It is conventional to transform that mechanical energy into electricity thanks to a generator driven by the expander.
However, in many applications, the electricity produced with this system may exceed the electrical needs of the vehicle and, consequently, may not be fully used.
On the other hand, using the energy recovered by this system in the form of mechanical energy, for example by connecting the expander to the driveline of the vehicle, may involve the implementation of additional complex systems, which would make the arrangement more complex, would require space and ultimately bring weight and cost.
It therefore appears that engine arrangements comprising a waste heat recovery system which have been proposed for vehicles are not fully satisfactory and can be improved.
It is desirable to provide an improved internal combustion engine arrangement which can overcome the above mentioned drawbacks.
More specifically, it is desirable to provide an internal combustion engine arrangement for a vehicle comprising a waste heat recovery system which can allow better use of the energy recovered from the exhaust gases.
According to an aspect of the invention, such an internal combustion engine arrangement comprises:                an internal combustion reciprocating piston engine, and an exhaust line capable of collecting exhaust gases from said engine;        a waste heat recovery system carrying a working fluid in a loop, in which said fluid is successively compressed, heated in a heat exchanger by means of the exhaust gases, and expanded in a first expander;        a first compressor located in the exhaust line and mechanically connected to the first expander of the waste heat recovery system.        
Thus, in an internal combustion engine arrangement according to an aspect of the invention, the thermal energy of at least one engine fluid, such as the engine exhaust gases, EGR gases, engine cooling fluid, lubrication fluid, charged intake air, etc. . . . is converted by the waste heat recovery system into mechanical energy by the expander and is transferred in mechanical form from the expander of said waste heat recovery system towards a compressor provided in the exhaust line.
The recovered energy is used to compress the exhaust gases, or more particularly to benefit from the suction effect at the input of the compressor, in order to reduce the exhaust back pressure on the engine which is prejudicial to the engine efficiency. Such back pressure is all the more high as a fairly high number of devices are now commonly arranged in the exhaust line for various purposes, such as for reducing air pollution, for reducing noise and/or for recovering energy.
Therefore, the energy needed for reducing the exhaust back pressure is recovered by means of the waste heat recovery system without needing an intermediate form of energy transfer other than the mechanical energy transfer from the expander to the compressor.
Another advantage of an aspect of the invention is that it does not require expensive or complex implementations to connect the expander of the waste heat recovery system to the first compressor.